Some of the roman weapons were plain wrought iron too! "The Metallography or Early Ferrous Edge Tools and Edged Weapons" has an example IIRC.
The Romans also used piling as well.
As for the lower temp deal. Think of cast iron---melts a lot lower than steel does and the difference is only carbon content, cast iron has a lot more carbon than high carbon steel! Or high school chemistry---the more crud is in something the lower it's melting point is and higher it's boiling point. One example is solder: add tin to the lead and the MP goes down.
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Thomas
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